• Journal of the Korea Concrete Institute
• /
• v.17 no.5 s.89
• /
• pp.857-868
• /
• 2005

This paper deals with the accumulated damage in concrete structures due to the cyclic freeze-thaw as an environmental load. The cyclic ice body nucleation and growth processes in porous systems are affected by the thermo-physical and mass transport properties, and gradients of temperature and chemical potentials. Furthermore, the diffusivity of deicing chemicals shows significantly higher value under cyclic freeze-thaw conditions. Consequently, the disintegration of concrete structures is aggravated at marine environments, higher altitudes, and northern areas. However, the properties of cyclic freeze-thaw with crack growth and diffusion of chloride ion effects are hard to be identified in tests, and there has been no analytic model for the combined degradations. The main objective is to determine the driving force and evaluate the reduced strength and stiffness by freeze-thaw. For the development of computational model of those coupled deterioration, micro-pore structure characterization, pore pressure based on the thermodynamic equilibrium, time and temperature dependent super-cooling with or without deicing salts, nonlinear-fracture constitutive relation for the evaluation of internal damage, and the effect of entrained air pores (EA) has been modeled numerically. As a result, the amount of ice volume with temperature dependent surface tensions, freezing pressure and resulting deformations, and cycle and temperature dependent pore volume has been calculated and compared with available test results. The developed computational program can be combined with DuCOM, which can calculate the early aged strength, heat of hydration, micro-pore volume, shrinkage, transportation of free water in concrete. Therefore, the developed model can be applied to evaluate those various practical degradation cases as well.

• Journal of the korean Society of Automotive Engineers
• /
• v.5 no.1
• /
• pp.45-53
• /
• 1983

There exist many kinds of frictions in internal combustion engine such as piston ring and skirt, cam and tappet, bearing friction etc. Among them, the frictions between piston ring, skirt and cylinder are particular. These frictions for motoring test are differ from that of firing test even though the temperature of cooling water and lubricating oil keep identically. The frictions for firing test are increased due to combustion pressure and products. The precise calculation of the friction is difficult. But we can assume that the friction is governed by the viscosity of lubricating oil and gas pressure of cylinder. And the viscosity of lubricating oil is dependant on gas temperature of cylinder, so the piston friction may be governed by gas pressure and temperature of cylinder. In this treatise, we propose the method of evaluating piston friction under the condition of constant engine speed, and we analyzed the behaviours and influence of factors concerned with the piston friction for output correction when the inlet pressure and temperature were varied. The main results are as follows: 1) The behaviours on the inlet conditions for the contact force of the piston rings and the viscosity of the lubricating oil concerned with piston friction are found. 2) The essential point the these behaviours is dependant on the cyclic variation following to the inlet conditions. 3) According to our analysis, It was observed that the viscosity of lubricating oil is more effective than the contact force to the piston rings.

• Journal of Biomedical Engineering Research
• /
• v.32 no.1
• /
• pp.32-36
• /
• 2011

The insufflators in endoscopic surgery supply carbon dioxide to make the air-filled cavity in the abdomen. It contains many kinds of pneumatic and electronic parts and they are connected with the air tubes and electrical wires. The printed circuit boards (PCB) perform wiring, holding and cooling tasks in electronic systems. In this study, the PCB is used as the air channel for insufflators to decrease the cost, volume, and the malfunction according to aging of the device. Three layers of PCB made of FR4 are combined with prepreg as adhesive which has the internal airway channel according to the design. By mounting the pressure sensors and valves, the PCB based fluidic system is implemented. After calibration of flow sensor, the flow rate of the gas also can be measured. The climate test, temperature test, and biocompatibility test showed this idea can be used in insufflators for laparoscopic surgery.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.53 no.6
• /
• pp.17-22
• /
• 2011

Biomass gasification provides synthesis gas or syngas that can be used for internal combustion engines as fuel or chemical synthesis as feedstock. Among different types of gasifiers, downdraft gasifier can produce relatively clean syngas with lower tar contents. In this study, a downdraft gasifier was fabricated with 150 mm of hearth diameter to gasify woodchip that is commercially available in this country. After drying woodchip to about 20 %, gasification experiments were conducted measuring temperature, pressure, air and gas flow rates. The volumetric concentrations of CO, $H_2$, $CO_2$, $CH_4$ were 10.7~14.5, 16.5~21.4, 12.5~16.6, and 2.3~2.9, respectively. They were overall within the ranges of the results that the previous studies showed. However, CO concentration was relatively lower and H2 was slightly higher than those from other studies. It seemed that water gas shift reaction was occurred due to the moisture in the fuel woodchip. Additional drying process coupled with syngas cooling would be required to improve the overall efficiency and syngas quality.

• Proceedings of the KIPE Conference
• /
• 2004.07b
• /
• pp.992-996
• /
• 2004

Small electric motors in an automobile perform various tasks such as engine cooling, pumping, and in heating, ventilating, and air-conditioning (HVAC) system. At present, most of dc motors are supplied by 12V or 24V batteries. However, DC motors surfer from lack of efficiency, low life cycles and unreliability. Therefore, there is a growing interest in substituting DC motors for advanced AC motors including switched reluctance motors. Although there are several other forms SRM converters, they are either unsatisfactory to the control performance or unsuitable for the 12V-battery powered 3-phase SRM drives. Taking into account the requirement for effective operation and simplicity structure of converter in the limited internal environment of automobiles, the author inclines toward selecting the modified C-dump converter as well as the energy efficient C-dump converter. This is so that more economical and efficient converter topology in automobile industries can be utilized. This paper describes the foundation for the design and development of a 12V-250W-3000rpm SRM drives for automobiles. Furthermore, complete circuit, computer simulation and experiment results are presented to verify the performance of the C-dump converters.

• KIEAE Journal
• /
• v.15 no.2
• /
• pp.117-122
• /
• 2015

Purpose: Generally, 30% of the total energy consumption in office building is used for artificial indoor lightings, and almost 75-85% of electric power in fluorescent and Light-Emitting Diode (LED) lightings can be dissipated as a form of heat into indoor environment. The heat generated by indoor lightings can cause the increase of cooling load in office buildings. Thus, it its important to consider indoor lightings as a heat and light source, simultaneously. Method: In this study, we installed two kinds of indoor lightings including fluorescent and LED lightings and measured surface temperature of both indoor lightings. In addition, we obtained ambient temperature of indoor space and finally calculated total heat dissipated from plenum area and surface of lightings. Result: Total indoor heat gain was 87.17Wh and 201.36Wh in cases of six 40W-LED lightings and 64W-fluorescent lightings, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1993.11a
• /
• pp.137-140
• /
• 1993

Electrical properties and thermal annealing effects of $C_{22}$-quinolium(TCNQ) Langmuir-Blodgett(LB) films were studied. Typical current-voltage(I-V) characteristics along the perpendicular direction chow an anomalous behavior of breakdown near the electric-field strength of $10^{6}$V/cm. To see the thermal influence of the specimen, current was measured as a function of temperature(20∼$180^{\circ}C$). It shows that the current increases about 4 orders of magnitude near 60∼$70^{\circ}C$ and remains constant far a while up to ∼$150^{\circ}C$ and then suddenly drops. Such increase of current near 60∼$70^{\circ}C$ seems tn be related to a softness of alkyl chains. Besides the electrical measurements, UV/visible absorption(300∼800 nm) of the thermally annealed sample was measured to see the internal-structure change. It is found that there are four characteristic peaks. At 494 nm, the optical absorption of the thermally annealed specimen at $60^{\circ}C$ starts increase and stays almost constant upto∼ $140^{\circ}C$. And eventually it disappears above $180^{\circ}C$. After heat treatment of the specimen up to $150^{\circ}C$, Uv/visible absorption was measured while cooling.

• 한국태양에너지학회:학술대회논문집
• /
• 2008.11a
• /
• pp.190-195
• /
• 2008

The objective of this research is to determine overall heat transfer coefficients (K-value) of exterior wall, floor, and roof of Nakseonjae, a Korean traditional residence via field measurement of transient heat flow and temperature difference across each envelope component. Heat flow sensors and T-type thermocouple were attached on the internal and the external surface of each building component, and real-time measurement data were collected for the three consecutive summer days. The K-values determined in this research showed good agreement with other results from open literature. Peak and annual thermal loads of the traditional residence estimated by a commercial energy simulation program were compared with those for a current apartment house. The traditional house showed lower annual cooling load than that of the current building. It may caused by the fact that the traditional building has less air-tight envelopes and no fenestration passing direct solar radiation into the space.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2011.05a
• /
• pp.50.1-50.1
• /
• 2011

Lead-free ceramics with a composition of 0.55 mol%$K_4CuNb_8O_23-(K_{1-x}Na_x)NbO_3$ (KCN-KNNx) where $0.45{\leq}x{\leq}0.60$ were synthesized by conventional ceramic processing. Results revealed that the addition of Na was effective in changing the microstructure and relative density of KCN-KNNx. Further, the addition of Na resulted in a slight shift of the phase transition temperatures (To-t and Tc) toward low values. A high mechanical quality factor (Qm) of 1850 was found atx=0.54, which might be due to the build-up of an internal bias field (Ei) within KCN. Thermal hysteresis in KNNx was confirmed with an increase in the Na content during the heating and cooling cycles, resulting from structural changes. Thus, KCN-KNNx with x=0.54 exhibits excellent piezoelectric properties with d33 (97 pC/N), kp (36%), and Qm (1850), being promising candidates for application in high-power piezoelectric devices.

• Journal of computational fluids engineering
• /
• v.20 no.1
• /
• pp.39-46
• /
• 2015

In this research, we studied the pressure drop affecting on the internal surface roughness and the curvature radius of a U-tube, which is used for the cooling system in PWR(Pressurized Water Reactor). Using ANSYS-FLUENT, a commercial code based on CFD(Computational Fluid Dynamics) technique, we compared a Moody chart with the Darcy friction factor changed by a range of various surface roughness and Reynolds numbers of a straight pipe model. We studied the effect giving variation about a range of various surface roughness and the curvature radius of the full scale U-tube model. The material of the heat transfer tube is Inconel 690 used in the steam generator. We compared the velocity distribution of selected 4 locations, and derived the correlation between the surface roughness and the pressure drop for the U-tube of each representative curvature radius using the linear regression method.